1. Field of the Invention
The present invention relates to a communication processing technique in a communication system including a terminal of a non-continuous connection.
2. Description of Related Art
As a connection mode of a terminal to a network, a continuous connection and a non-continuous connection are given as examples. When a terminal is continuously connected to a network, a fixed IP address can be assigned to the terminal. Accordingly, in a communication system including a continuously connected terminal, communication can be performed by establishing a TCP connection to this terminal at an arbitrary time. Meanwhile, when the terminal is non-continuously connected to the network, the IP address of the terminal is not fixed, and therefore skill is required for making communication to this terminal. For example, when the terminal is connected to the network through a dial-up, the IP address is assigned to this terminal from a dial-up server every time the dial-up connection is made. Accordingly, the TCP connection cannot be established to this terminal at an arbitrary time.
Japanese Patent Laid-Open Publication No. 2005-210575 proposes a technique for promptly making data communication even when a terminal without a fixed IP address is included in an information system. Specifically, in Japanese Patent Laid-Open Publication No. 2005-210575, a continuously fixed IP address is not assigned to an IP adapter 40. This IP adapter 40 periodically transmits a UDP packet to a server 42, and periodically reports the IP address of its own device. Then, when a control request signal is generated to the server 42 from a cellular phone 44, the server 42 can instantly connect with the IP adapter 40, because the IP address of the IP adapter 40 is known. Thus, when a trigger of processing is generated from the cellular phone 44, it is possible to perform data communication promptly through the server 42 and the IP adapter 40.
As described above, when the terminal making a non-continuous connection is included in the communication system, skill is required for making connection to this terminal. According to Japanese Patent Laid-Open Publication No. 2005-210575, the UDP packet is periodically transmitted to the server by the terminal (IP adapter 40) on a receiving side, thereby continuously reporting the IP address of its own device.
However, the terminal on the receiving side must continue to send the UDP packet all the time. Even if a transmission request from a transmitting side is not generated, the UDP packet must be continuously sent to the server, and this is inefficient.
Also, for example, when there are a plurality of terminals non-continuously connected to the communication system, the UDP packet is continuously transmitted to the server from all of these terminals, and this is not only inefficient but also imposes a substantial load on the server.
In addition, when a non-continuous communication line network is used, another problem is involved. In a line network of the non-continuous communication, in some cases, it is difficult for a particular terminal to maintain a communication state. For example, in order to provide a service to many users, the line in which no traffic is generated for a prescribed time is sometimes disconnected. When the transmission of a packet is not performed for a prescribed time, this line may sometimes be disconnected depending on the type of the dial-up router.
In this way, in the communication system including the terminal of the non-continuous connection, first, skill is required for making a communicable state promptly, and further skill is required for maintaining the communication state until transmission and reception of required information is completed. This is because when a communication error, etc. occurs in the middle of the transmission and reception of data, a recovery processing is required, thus involving a complicated processing.
Therefore, in view of the above-described problems, an object of the present invention is to provide a technique capable of promptly and efficiently starting communication processing when a demand for communication is generated, in a communication system including the terminal of the non-continuous connection.
In addition, another object of the present invention is to provide a technique for promptly and efficiently starting the communication processing when the demand for communication is generated and for normally completing the communication, in a communication system including the terminal of the non-continuous connection.